Liquid crystal display devices have been used for watches and electronic calculators, various measuring apparatuses, automotive panels, word processors, electronic notebooks, printers, computers, televisions, watches, advertising displays, etc. Typical examples of a liquid crystal display mode include a TN (twisted nematic) mode, a STN (super-twisted nematic) mode, a vertical alignment mode and an IPS (in-plane switching) mode using TFT (thin-film transistor), and the like. Liquid crystal compositions used for these liquid crystal display devices are required to have stability to external factors such as moisture, air, heat, light, and the like, exhibit a liquid crystal phase (nematic phase, smectic phase, blue phase, and the like) within as wide a temperature range as possible including room temperature as a center, and have low viscosity and low drive voltage. Further, each of the liquid crystal compositions is composed of several types to several tens types of compounds selected in order to have optimum values of dielectric anisotropy (Δ∈) and refractive index anisotropy (Δn) for a display device.
A horizontal alignment-mode display, such as a TN mode, a STN mode, an IPS mode, or the like, uses a liquid crystal composition having positive Δ∈. Also, there has been reported a driving method in which a liquid crystal composition having positive Δ∈ is vertically aligned with no voltage applied, and display is performed by applying a transverse electric field, and the need for a liquid crystal composition having positive Δ∈ is further increased. On the other hand, improvement in response speed is required for all driving methods, and a liquid crystal composition having lower viscosity than existing ones is required for solving the problem. In order to produce a liquid crystal composition having low viscosity, it is effective to decrease the viscosity of each of polar compounds constituting a liquid crystal composition. Also, when a liquid crystal composition is used for a display device or the like, it is required that a stable liquid crystal phase is exhibited over a wide temperature range. In order to maintain a liquid crystal phase over a wide temperature range, each of components constituting a liquid crystal composition is required to have high miscibility with other components and high clearing point (T→i).
In order to produce a compound having high T→i, it is generally known to be preferred to introduce three or more ring structures such as a 1,4-cyclohexylene group, a 1,4-phenylene group, or the like. On the other hand, in order to produce a compound having low viscosity, a compound having a plurality of ring structures which are directly bonded to each other without through a linkage group, that is, a compound referred to as a “directly-bonded ring system”, is preferred. However, in general, directly-bonded ring-system compounds having three or more ring structures and positive Δ∈ frequently have high crystallinity and low miscibility with a liquid crystal composition. In order to improve the problem, compounds containing various linkage groups introduced therein have been studied. It has been found that viscosity is slightly increased by introducing a linkage group, but miscibility with a liquid crystal composition can be improved (Patent Literatures 1 to 8). However, compounds having a —CH2O— group as a linkage group exhibit high chemical stability and high solubility in liquid crystal compositions but have high viscosity and the problem of significantly decreasing T→i.